This invention relates to the field of projectiles and more particularly to an apparatus and method for determining the roll attitude of a projectile with respect to a fixed local coordinate system.
Modern weapons often require knowledge of their attitude in space for control purposes. The actual roll orientation of a body with respect to a local coordinate system may be used for a number of purposes. For example, roll orientation of a directional air bursting munition is desirable to achieve proper fragmentation placement upon detonation. Thus, detonation of a directional air bursting munition desirably occurs at a particular roll orientation with respect to the environment. Additionally, the actual roll orientation of a projectile may be considered in the activation of divert mechanisms used to steer a weapon toward a desired target.
Systems for determining the attitude of a weapon have included side mounted sensors, such as radar, for determining the relative presence or absence of ground beneath the sensor, gyroscopic and angle-rate sensors to determine the body pitch-over that occurs as a weapon falls due to gravity, inertial sensors calibrated prior to launch that remember the original attitude reference, and the like.
The aforementioned methods of sensing projectile attitude in modern weapons systems include various drawbacks. Inertial sensors are generally not useful in spin stabilized projectiles. Expensive and delicate sensors add to the cost of each weapon and can suffer damage associated with high launch forces and high in-flight temperatures. The marginal cost of such added components can often outweigh the associated marginal benefit.
It would be desirable to provide a system for determining roll orientation of a weapon using low cost sensors and electronics. Desirably, the system may utilize components that are already included in the projectile fuzing system. Further, it would be desirable for such a system to have no moving parts.